Stable polyacetaldehydes and process for the production thereof



United States Patent 3,288,758 STABLE POLYACETALDEHYDES AND PROCESS FORTHE PRODUCTION THEREOF Maurice Joseph Amand Letort, Paris, and BernardFleureau, Verneuil-en-Halatte, France, assignors to Charbonnages deFrance, Paris, France, a public institution of France No Drawing. FiledJune 11, 1965, S81. No. 463,355 Claims priority, application France,Apr. 21, 1960, 824,961; Nov. 9, 1964, 994,366 18 Claims. (Cl. 260-67)The present application is a continuation-in-part of applicantscopending application Serial No. 101,640, filed April 19, 1961, nowabandoned.

The present invention relates to elastomer polymers of acetaldehydehaving high thermal stability and the method of obtaining them.

It is known that acetaldehyde polymerized by various methods such ascrystallization, the action of borofiuoride and the like, results in theformation of elastomer polymers. Unfortunately the thermal decompositionrate of these polymers even at temperatures in the range of 60- 70 C. isvery high, which prevents their being utilized industrially.

For a long time it was believed that the crystallization was necessaryfor forming polyacetaldehyde. It is now known that such is not the caseand that the polymer can be obtained at temperatures much higher thanthat of crystallization.

Whatever the conditions in which they are prepared, known polymersalways appear in the same way: rubbery white grains having a tendency toagglomerate. These polymers have excellent physical properties, makingthem suitable for valuable industrial applications. Unfortunately, theydecompose easily under the action of heat or acids. Various attemptshave already been made to increase the heat-resistance ofpolyacetaldehydes by the addition of products such as sodium carbonatesor bicarbonates, amines, ureas, naphthols, hydroquinones, etc. Now, thepresent invention relates to polymers having greatly improved thermalstability compared with that of polymers produced by previous knownmethods, thus allowing for applications which it was not possible toenvisage with the polymers known at present.

It is an object of the present invention to provide elastomersofpolyacetaldehyde of high molecular weight, stabilized and stable up toa decomposition starting temperature of at least 85 C.

It is a further object of the present invention to provide elastomers ofpolyacetaldehyde of high molecular weight, improved in such a way thatthey are stabilized and remain stable up to a decomposition startingtemperature of at least 125 C.

A still further object of the present invention is to provide novelprocesses for the thermal stabilization of elastomers of acetaldehyde ofhigh molecular weight.

The present invention thus relates to a process for stabilizingacetaldehyde elastomers of high molecular weight having an originaldecomposition starting temperature of about 55 C. by intimatelycontacting the elastomers in an alkaline aqueous solution, such asalkaline metal hydroxides, carbonates and bicarbonates, and separatingthe elastomers thus treated to yield a stabilized elasto-mer having adecomposition starting temperature of at least 85 C. The alkaline metalcompounds can be sodium, potassium lithium compounds.

The present invention also relates to a process for stabilizingacetaldehyde elastomers of high molecular weight by dissolving theelastomer in a solvent for the elastomer, allowing the resultingsolution to stand at room temperature and then adding the alkalineaqueous solution in ac- "ice cordance with the previous paragraph.Examples of the solvent may be pyridine, dimethylformamide and acetone.

Acetaldehyde elastomers having even higher decompositionstartingtemperatures of at least 125 C. are obtained when acet'canhydride is added to the solution of the elastomer in the solventbefore the treatment with the alkaline aqueous solution.

Elastomers of acetaldehyde which have been stabilized as indicatedheretofore can be stabilized still further up to decomposition startingtemperatures as high as 191 C. by a heat treatment step either in vacuumor in a stream of an inert gas.

It is known that it is possible to stabilize crystalline polymers ofaldehydes such as butyraldehyde by heating. However; when this method isapplied to polyacetaldehydes without taking special precautions,decomposition follows according to a law of first order and nostabilization occurs as was shown, for example, in United States PatentNo. 3,001,966 of September 18, 1962.

Applicants have now discovered that, very surprisingly, polymers ofacetaldehyde previously treated by an aque- Ous solution of carbonate,bicarbonate or hydroxide of an alkaline metal, and then heated in vacuumor in a stream of inert gas, no longer decompose according to a law offirst order and give new polymers of acetaldehyde having great thermalstability.

Acetaldehyde polymers are stabilized by a process in accordance with thepresent invention by applying the following operation procedure:immediately after being prepared, the polyacetaldehyde is placed in thesolvent. It swells slowly and must be left until complete dissolutionoccurs (generally several hours). In some of the examples, the polymerput into solution in the solvent is treated with acetic anhydride.Generally, equal volumes of acetic anhydride and solvent are used, butthe volume ratio is not critical.

The treatments are carried out under nitrogen to prevent oxidationreactions and with stirring to facilitate contact between the reactants.

At the end of the time selected as reaction duration, the polymersolution is poured into a solution of the alkaline material in order toensure, on the one hand, the precipitation with water of polymer and, onthe other hand, the neutralization, if required, of the aceticanhydride. The polyacetaldehyde is thereafter recovered and subjected tothorough washing in water.

The crude or unstable polyacetaldehyde may be treated with the solutionof carbonate, bicarbonate or hydroxide of an alkaline metal, bysubmitting it to energetic washing, preferably with a turbo-stirrer orother apparatus ensurmg efiicient grinding and stirring without the useof the solvent.

Polymers of acetaldehyde which may be treated according to the inventioninclude all polya-cetaldehydes whether or not they have beenstructurally modified, as for example, by treating by means of acarboxylic anhydride such as acetic anhydride. 7

The temperature of the heat treatment step is selected in order thatdegradation 'does not occur too rapidly to be controlled or too slowlyto result in stabilization in a reasonable length oftirne. In general,temperatures of from to 300 C. meet these requirements. The length oftreatment will be a function of the temperature and the degree ofthermal stability desired, stabilization only being obtained by the lossof part of the polyacetaldehyde.

Products stabilized by heat treatment in this manner undergo a loss ofweight'of less than 6%, and even of less than 1% per hour when they areheated to 138 C. in an inert atmosphere. Here, as in the descriptionwhich follows, the expression loss of weight per hour means a 8,2 (I Qloss of weight observed on the sample after heating at the temperaturegiven for one hour.

The full significance and advantages of the invention will be apparentfrom the following examples wherein the decomposition startingtemperature (D.S.T.) is that at which the polymer has lost 0.025% of itsinitial weight when a sample of polymer is heated in a furnace of whichthe regulating system is such that the temperature increases inaccordance with a linear law as a function of time, the heating ratebeing adjusted to 1 C. per minute and the test being carried out in anitrogen atmosphere.

Another standard for measuring thermal stability of the polyacetaldehydeelastomers, is determining rate constants for the thermal degradationreaction at temperatures such as 138 C. and 160 C. The procedurefollowed in making the determinations of rate constant was as follows:

A sample of polyacetaldehyde elastomer was placed in a vessel andweighed. The air in the vessel was displaced by nitrogen. The vessel wasthen placed in a furnace provided with a regulating system and usingcontrolling balances. The temperature of the furnace is maintainedconstant at the temperature being measured, e.g. 138 C. or 160 C., for apredetermined time in a nitrogen stream. The vessel is weighed. Byrepeating the experiment for different intervals of time and calpulatingthe weight percent remaining with time and plotting the log percentremaining against time, one derives a curve whose slope defines the rateconstant for thermal degradation. This may be expressed mathematicallyby the equation:

k in percent per mn.=2.3 X 100 where p =percentage of weight remainingat time t where p =percentage of weight remaining at time 1 In the caseof polyacetaldehyde elastomers which have not been treated in accordancewith the present invention, the k is first order, whereas forpolyacetaldehyde elastomers stabilized in accordance with the presentinvention do not decompose according to a law of first order.

EXAMPLE 1 A pure acetaldehyde monomer was prepared by decomposition ofparaldehyde occurring at about 80 C. in the presence of traces ofphosphoric or sulfuric acid. The vapors flow through a column packedwith refractory materials externally cooled with water so as to ensurethe reflux of the entrained paraldehyde.

The crude monomer thus obtained was then distilled in a packed columnunder a slight nitrogen pressure and purified (by being passed overcopper dispersed on Kieselguhr and heated to 180 C.) to preclude anyrisk of oxidation.

The thus-purified monomer was cooled to a temperature slightly lowerthan its freezing point (-123.3" C.) and thereafter reheated. Agelatinous mass of polyacetaldehyde swollen with monomer was obtained.The polymer was washed with petroleum ether to drive out the monomer anda rubbery, only slightly sticky, white polyacetaldehyde was recovered.

The yield was of about 25% 40 parts of this polymer were dissolved in600 parts of pyridine over 21 hours. Then, the polymer was precipitatedby adding 2000 parts of an aqueous solution of sodium carbonate. Thepolymer formed was recovered and thoroughly washed with water.

The decomposition starting temperature of the product obtained was 105C.

EXAMPLE 2 Monomer acetaldehyde is prepared by decomposing paraldehyde ata temperature of about 80 C. in the presence of traces of concentratedsulphuric acid. The

monomer obtained is purified by distillation in a filling, column underslight pressure of nitrogen.

The monomer thus purified contains traces of acid and is cooled to alittle below its freezing point (123.3 Q)

and then warmed. A gelatinous mass of crude polyacetaldehyde swollenwith monomer is obtained. This crude polymer is divided into threefractions which are freed from their monomer by washing in aturbo-stirrer, changing the washing liquid 5 times and using on eachoccasion 500 parts by weight of this liquid per part by Weight ofpolymer; the first fraction is washed with demineralized water, thesecond fraction with petroleum ether and the third with carbonated watercontaining 20 g. of Na CO -10H O per litre.

The three samples are dried in vacuum at room temperature for 24 hours;the yield in polymer with respect to the initial monomer is about 40%The decomposition starting temperature test was carried out on afraction of each sample and the following results were obtained:

Polymer washed with dernineralized water, D.S.T.=57 C. Polymer washedwith petroleum ether, D.S.T.=55 C. Polymer treated with sodiumcarbonate, D.S.T.==l00 C.

EXAMPLE 3 (A) The starting polymer obtained as in Example 2 is dividedinto two fractions one of which is treated by 50 parts by weight of anaqueous solution at 5 g. per litre of NaHCO per part by weight ofpolymer, and the other fraction by the same quantity of an aqueoussolution at 5 g./ litre of K CO After drying in vacuum at roomtemperature for 24 hours, a sample of the fraction treated by NaHCOgives a D.S.T. of 100 C. and a sample of the fraction treated by K COgives a D.S.T. of 90 C.

(B) Example 3 (A) is repeated using Li CO- and LiOl-I instead of K COand NaHCO respectively.

The polymer treated by Li CO has a decomposition starting temperature ofC.

The polymer treated by LiOH has a decomposition starting temperature of95 C.

EXAMPLE 4 C. For the polymer treated by dernineralized Water 58 For thepolymer treated by NaOH For the polymer treated by KOH EXAMPLE 5Nitrogen is passed through a 1 litre reactor provided with a stirrer, athermometer and a gas inlet and outlet, and exteriorly cooled by amixture of petroleum ether and liquid nitrogen. A stream of ethylene inthe reactor causes this gas to condense, 200 g. of liquid acetaldehyde,distilled and purified as in Example 2, are added and a. temperature offrom C. and C. is applied- 1 cm. of etherate of BB, is injected with asyringe, polymerization starts after a few minutes and the stirrerisblocked. The temperature is held below 120 C. forone hour andpolymerization is stopped by the slow addition of 80 g. of triethylaminemixed with 600 g. of pyridine.

A fraction of this consistent paste (25 grams) is washed by hand fivetimes with iced demineralized water (using two litres of water eachtime) and another 25 gram frac tion is washed in the same manner withcarbonated water at 20 g. of N21 CO -1OH O per litre (also using twolitres of carbonated water each time). These fractions are,

then dried in vacuum for 24 hours at a normal temperature then treatedand tested as in Example 2.

Polymer washed with demineralized water, D.S.T.=75 C. Polymer washedwith Na CO D.S.T.= 100 C.

EXAMPLE 6 Polyacetaldehyde is prepared by the melting "point method asdescribed in Example 2. The resulting polymer is washed in demineralizedwater (500 parts by weight per part of weight of polymer) a sample ofthis polymer is dried as on Example 2. The decomposition startingtemperature determined is 58 C. The Whole remaining polymer is dividedinto three fractions which are dissolved Polymer dissolved in: C.Pyridine and treated by Na CO 105 Dimethylformamide and treated by K CO85 Dimethylformamide and treated by NaHCO 105 Acetone and treated byKHCO 90 EXAMPLE 7 The pyridine solution of the polymer obtained in thepreceding example was placed into a reactor permitting the flow of acurrent of nitrogen therethrough, having stirring means, and 700 partsof acetic anhydride were added.

The reactants were maintained in contact for 20 hours, during which timethe solution gradually darkened.

At the end of this period it was poured into a saturated solution ofsodium carbonate in water; the polymer was precipitated; it wasrecovered and thoroughly washed with water.

The decomposition starting temperature of the product obtainedwas 127 C.

The influence of the different factors in the treatments disclosed inthis example will be better appreciated when it is pointed out that thedecomposition starting temperature of the untreated polymer is 55 C. andthat of polymer dissolved in pyridine and thereafter precipitated withwater is about 65 C.

EXAMPLE 8 The conditions of Example 7 were exactly reproduced but thecontact time between the reactants was extended to 33 days.

The same decomposition starting temperature was ob tained.

EXAMPLE 9 The conditions of Example 7 were reproduced using a reactionduration of 96 hours, at the end of which the polymer decompositionstarting temperature was 125 C.

The temperature was then brought to 60 C. and held for 18 hours. Thedecomposition starting temperature then falls to 105 C. After removingthe degradation products by dissolving in acetone and precipitation withwater again, the decomposition starting temperature was 122 C.

- EXAMPLE 10 The conditions of Example 7 were reproduced but with theaddition of 0.1 part of anhydrous sodium acetate, which is a knowncatalyst in acetylation reactions.

The decomposition starting temperature was again 127 C.

6 EXAMPLE 11 perature for 24 hours. The solution is divided into threefractions, the first, fraction A is precipitated using demineralizediced Water, the precipitate being washed twice With demineralized water,using 500 parts by weight per part by weight of polymer each time. Thesecond fraction B is precipitated with carbonated water containing 15 g.of Na CO -10H O per litre, then washed twice by a solution of the sameconcentration, 500 parts by weight of carbonated water per part byweight of polymer being used for each wash. The third fraction C isprecipitated by a solution at 15 g. per litre of (NH CO then washedtwice by the same solution (each time 500 parts by weight of solutionper part by weight of polymer).

The first fraction A treated by demineralized water is divided intothree parts, a, b and c. The first (a) is kept as a control. Itsdecomposition starting temperature is 56 C. The second (b) is dissolvedin 7.1 parts of ether containing 0.01 part of pyridine with respect tothe weight of polymer. The solution is stirred for 18 hours at roomtemperature, then the ether is eliminated by distillation on a coldsurface to leave polyacetaldehyde containing about 1% of pyridine. Itsdecomposition starting temperature is 62 C. The third part (c) istreated in the same manner as the second but replacing pyridine bydiphenylamine. The decomposition starting temperature of the polymer is64 C.

Heated to 138 C. or 160 C. in a nitrogen stream these three polymers (a,b, c) decompose in accordance with a law of first order giving K of 4and 5 and K in the range of 10.

The decomposition starting temperature of the polymer of fraction (0)treated by ammonium carbonate is 70 C. and when this polymer is heatedto 160 C. in nitrogen, its decomposition occurs without showingstabilization.

Thedecornposition starting temperature of the polymer of fraction ([1)treated by Na CO is 140 C. This polymer loses 17.7% of its Weight in anhour at C. and 28.7% at 180 C. Decomposition does not occur according toa law of first order; the product stabilizes by heating. After 24 hoursof treatment at 160 C., 58.3% of the initial weight of a polymer remainslosing 1.6% in an hour at 160 C. and 5.2% at 180 C. The decompositionstarting temperature was found to be C.

It can thus be seen that pyridine, diphenylamine or ammonium carbonatedo not enable elastorner polyacetaldehyde to be stabilized by heating.

EXAMPLE 12 The three samples prepared according to Example 2 areheat-treated at 138 C. in a nitrogen stream, the loss in Weight as afunction of time being registered on a thermal balance. The first twosamples decompose in accordance with a law of first order.

The sample washed with demineralized water gives a k of 3.86; the samplewashed with petroleum ether a k of 5.68; the sample treated by thesodium carbonate solution does not decompose according to a law of firstorder. It loses 22% of its weight in one hour during the first hourattaining a D.S.T. of 110 C. After 6 hours of heating at 138 C. therestill remains 39% of the initial Weight of a polymer the decompositionrate of which is now only 6.4% per hour (D.S.T. of 120 C.); after 12hours of heating there remains 31.5% of a polymer only losing 3.1%. perhourat 138 C. in nitrogen 7 If this fraction is subjected to heattreatment at 160 C. the loss in weight during the first hour is 54%.After 6 hours of treatment 16% of the initial weight of polymer:remains. Its rate of decomposition is then 12.5% per hour at 160 C.(D.S.T.=l34 C.).

gen stream decomposes according to a law of first order and gives a 1:of 8.68. The second fraction does not decompose according to a law offirst order, the loss in weight being 43% during 1 hour. After 6 hours20% of a polymer remains which only loses per hour A polymer obtained asdescribed in Example 2 is di- EXAMPLE 14 v1ded into two fractions; thefirst fraction is washed 5 tunes with demineralized Water by aturbo-stirrer using The polymers of Example 3(A) and 3(B) are submitted50 parts by weight of Water per part by weight of polymer. to heattreatment under nitrogen at 138 and 160 C. re- A sample .of this firstfraction is dried in vacuum at room spectively. Table I below gives theresults obtained.

Table I Fraction treated by NaHOO Length of Loss of Weight, percent/h.Temperature, treatment Yield,

C. in hours percent 138 C. D.S.T. 160 0. D.S.T.

100 13s 5 27 3 119 13s 12 23.5 2.1 13s 24 18.5 1.3 133 160 1 25 160 512.5 160 12 7.5 FRACTION TREATED BY K2001 FRACTION TREATED BY LnOO:

100 90 85 13s 0. 5 33 52 90 13s 1 10 40 106 13s 3 5.5 15 110 FRACTIONTREATED BY LiOH I 13s 1 ,23 69. 5 103 13s 3 4 12 117 150 1 6 r 15.7 127temperature for 24 hours. The decomposition starting EXAMPLE 15temperature obtained is 52 C. The second fraction is washed in the samefashion but with a solution of car- 50 The fractions of Example 4treated by soda or potash bonated water at 5 g. per litre of Na CO -10HO. The are submitted to heat treatment at 138 C. or 160 C. decompositionstarting temperature of a dried sample is in nitrogen. 102 C. The firstfraction heated at 138 C. in a nitro- The results obtained are given inTable II below.

Table II Temper- Fraction ature 01 Length of Yield, K Km treatmenttreatment percent in C. 1'11 hours Treated by demineralized Water" 1002. 34 6. 14

Treated NaOH Loss in weight, percent/h.

138 C. D.S.'l. 160 C. D.S.T.

Treated KOH EXAMPLE 16 The fraction of Example treated by demineralizediced water decomposed when heated at 138 C. according to a law of firstorder. The fraction treated by N21 CO is more stable and stabilizesfurther after heat treatment.

The results obtained are shown in Table III.

1% fraction being treated by demineralized water, the followingfractions by solutions containing guper litre respectively of-K CO Na CO-10H O, KHCO NaHCO NaOH, KOH and LiOH each washing being carried outbyusing 500 parts by weight of the Washing solution per part by weightof polymer.

Table III 'lemper- Length of Yield, Fraction ature of treatment percentK111 Km treatment in hours in C.

Treated by demineralized water 100 1. 36 8. 06

Loss of Weight, percent/h.

111 C. D.S.T. 138 C. D.S.T.

Treated by N21100: 100 10 52 100 138 3 l5 113 EXAMPLE 17 Table IV givesthe results obtained by submitting samples of the polymers of Example 6to heat treatment.

The decomposition starting temperatures are the following:

Table IV Temp. of Length of Yield, Polymer Treatment Treatment PercentKias K150 in C. in Hours Initial sample before dissoluti0n 100 2. 34 6.14

Loss of Weight, Percent/h.

138 D.S.T. 160 D.s.T.

After dissolution in pyridine and repreeipitation by NazCOa-lO H1O 10049 1 105 105 138 3 18 5 18. 9 114 138 6 14 2.4 133 160 1 15 26.7 132 1606 9 4.6 143 After dissolution in dimethylform-amide and reprecipitationby KzCO After dissolution in dimethylformamide and repreeipitation byNil/H003. 42 89 105 138 3 24 29. 2 138 6 13 1.2 134 160 1 17 32.4 119160 3 10 15 132 150 6 8 7 141 After dissolution in acetone andreprecipitation by KHCO3 EXAMPLE 18 C. Polymer treated by demineralizedwater 53 The polymer obtained by the crystal melting method 15 Polymer tt d b K 60 135 Washed with a sodium carbonate solution, dried, redis- 70Polymer tr ted by N CQ 140 solved in pyridine, then treated for 24 hoursby ac ti Polymer treated by KHCOg anhydride at room temperature, theproportions being 1 Polymer treated by NaHCO 130 part of aceticanhydride and 19 parts of pyridine for one Polymer treated by NaOH partof acetaldehyde. The solution is divided into 8 parts Polymer treatedbyKOH then precipitated and washed as in Example 11, the first 75Polymer treated by LiOH 140 1 1 On the other hand the first fractiondecomposes according to a law of first order, the others stabilize byheating.

Table V below gives the results obtained.

vacuum. The fraction treated by NaOH having a decomposition startingtemperature of 125 C. loses 30.1% at 160 C. in 1 hour in nitrogen; after24 hours of treat- Table V Temp. of Length of Yield, D.S.T., FractionTreatment Treatment Percent Km degrees in O. in Hours Treated bydemineralized water 100 8. 7 53 Loss of Weight in percent/hour Treatedby K; 100 9. 7 16. 3 33. 6 135 160 24 76. 2 2 2.1 B. 3 191 Treated by(30 N21 100 16. 1 42. 6 69. 7 140 160 24 41. 3 2. 3 ll. 4 35. 8 162Treated by COQHK 100 9. 8 18. 6 73. 1 130 160 24 26. 3 2. 1 4. 6 21. 4164 Treated by GO HNa 100 13. 7 32. 6 60 130 160 24 49. 2 l. 8 6. 26. 4160 Treated by NaOH 100 16. 8 29. 4 55. 5 135 160 24 47. 8 2.8 12. 7 35.4 159 Treated by KOH 100 8. 2 14. 9 35. 1 140 160 24 61.3 0. 6 3 18. 2172 Treated by LiOH 100 23. 6 43. 5 80. 5 140 160 24 85 5. 9 14. 5 39. 2156 EXAMPLE 19 ment at 160 C. in vacuum 16.5% of polymer remainsAcetaldehyde is polymerized by etherate of BF as described in Example 5.The paste recovered after addition of 80 g. of triethylamine and 600 g.of pyridine is dissolved in 1120 g. of pyridine. To parts by Weight ofthis solution is added one part by weight of acetic anhydride. Aftercontact at 25 C. for 24 hours the solution is divided into threefractions, the first being precipitated by iced demineralized water; thesecond is similarly treated by a solution of Na CO at 10 g. per litre;and the third by a solution of KHCO at 10 g. per litre, using 500 partsby weight of precipitated polymer for washing. The first fractiondecomposes according to a law of first order, the second and third arestabilized by heating in nitrogen. The results obtained are shown inTable VI.

which loses 35.2% of its weight in 1 hour at 180 C. in nitrogen and66.5% at 200 C. in 1 hour in nitrogen. The fraction treated by KHCOhaving a decomposition starting temperature of 130 C. loses 14.5% of itsweight in one hour when heated in nitrogen at 160 C. and 21.8% at 180 C.After treatment in vacuum for 24 hours at 160 C. there remains 64.3% ofa polymer which loses 2.5% at 160 C. for 1 hour in nitrogen, 5.5% at 180C., 25% at 200 C.

The polymers so obtained can be stabilized in air by amine or phenolicanti-oxidants. Decomposition rates in air similar to decomposition ratesin nitrogen are then obtained.

It is understood that the present invention has simply been described byway of example and without limitation Table VI Fraction treated bydemineralized Water 13.8.1. 0.

Length of Loss of Weight Percent/hour Temp., C. Treatment Yield, D.S.T.,in hours Percent degrees 160 C. 180 C. 200 C.

Fraction treated by Na OOa D.S.T.= C.

Fraction treated by KHCO D.S.T.=130 C.

EXAMPLE 20 and that useful alterations may be brought to it without Apolymer of acetaldehyde obtained by the melting point method is treatedas described in Example 18, precipitation and washing being carried outby utilizing 500 parts by Weight of a solution of NaOH or NaI-ICO at 10g. per litre per part by weight of precipitated polymer. The polymer isdried for 24 hours in vacuum at departing from the scope of theinvention.

What is claimed is:

1. Process for the thermal stabilization of polymers consisting ofpolyacetaldehyde elastomers of high molecular weight comprising treatingsaid elastomers with a dissolving amount of pyridine, allowing theresulting soluroom temperature and submitted to heat treatment in 75tion to stand at room temperature, adding an alkaline aqueous solutionselected from the group consisting of alkaline metal hydroxide,carbonates and bicarbonates solutions in an amount at least sufficientfor precipitating eifect, then separating the precipitated polymers fromsaid solution whereby a stabilized polymer having a decompositionstarting temperature of at least 85 C. is obtained.

2. Process for the thermal stabilization of polymers consisting ofpolyacetaldehyde elastomers of high molecular weight comprising treatingsaid elastomers with a dissolving amount of pyridine, allowing theresulting solution to stand at ambient temperature, adding an aqueoussolution of sodium carbonate in an amount at least sufiicient forprecipitating efiFect, then separating precipitated polymer from saidsolution, whereby a stabilized elastomer having a decomposition startingtemperature of at least 105 C. is obtained.

3. Process for the thermal stabilization of polymers consisting ofpolyacetaldehyde elastomers of high molecular weight comprising treatingsaid elastomers with a dissolving amount of pyridine, allowing theresulting solution to stand at ambient temperature, adding an aqueoussolution of sodium bicarbonate in an amount at least sufficient forprecipitating eifect, then separating precipitated polymer from saidsolution, whereby a stabilized elastomer having a decomposition startingtemperature of at least 105 is obtained.

4. Process for the thermal stabilization of polymers consisting ofpolyacetaldehyde elastomers of high molecular Weight comprising treatingsaid elastomers with a dissolving amount of pyridine in the presence ofacetic anhydride, allowing the solution to stand for a period of from 20hours up to several days, treating with an alkaline aqueous solutionselected from the group consisting of alkaline metal hydroxides,carbonates and bicarbonates solutions in an amount at least suflicientfor destroying the acetic anhydride and for precipitating said polymers,then separating the precipitated elastomers whereby a stabilizedelastomer having a decomposition starting temperature of at least 125 C.is obtained.

5. Process for the thermal stabilization of polymers consisting ofpolyacetaldehyde elastomers of high molecular weight comprising treatingsaid elastomers with a dissolving amount of pyridine in the presence ofacetic anhydride, allowing the solution to stand for a period of from 20hours up to several days, treating with an aqueous solution of sodiumcarbonate in an amount at least sufiicient for destroying the aceticanhydride and for precipitating said polymers, then separating theprecipitated elastomers, whereby a stabilized elastomer having adecomposition starting temperature of at least 125 C. is obtained.

6. Process for the thermal stabilization of polymers consisting ofpolyacetaldehyde elastomers of high molecular weight comprising treatingsaid elastomers with a dissolving amount of pyridine in the presence ofacetic anhydride, allowing the solution to stand for a period of from 20hours up to several days, treating with an aqueous solution of sodiumbicarbonate in an amount at least sufficient for destroying the aceticanhydride and for precipitating said polymers, then separating theprecipitated elastomers, whereby a stabilized ela'stomer having adecomposition starting temperature of at least 125 C. is obtained.

7. In a process for the thermal stabilization of polymers consisting ofpolyacetaldehyde elastomers by treating said polymers with pyridine andacetic anhydride, the improvement consisting in treating the reactionmedium comprising polyacetaldehyde dissolved in pyridine in the presenceof acetic anhydride with an alkaline aqueous solution selected from thegroup consisting of alkaline metal hydroxides, carbonates andbicarbonates solutions in an amount at least sufficient for destroyingthe acetic anhydride and for precipitating said polymer, and recoveringsaid precipitate, whereby stabilized pure elastomers having adecomposition starting temperature of at least 125 C. are obtained.

8. In a process for the thermal stabilization of polymers consisting ofpolyacetaldehyde elastomers by treating said polymers with pyridine andacetic anhydride, the improvement con-sisting in treating the reactionmedium, comprising polyacetaldehyde dissolved in pyridine in thepresence of acetic anhydride, with an aqueous solution of sodiumcarbonate in an amount at least sufficient for destroying the aceticanhydride and for precipitating said polymer, and recovering saidprecipitate, whereby stabilized pure elastomers having a decompositionstarting temperature of at least 125 C. are obtained.

9. In a process for the thermal stabilization of polymers consisting ofpolyacetaldehyde elastomers by treating said polymers with pyridine andacetic anhydride, the improvement consisting in treating the reactionmedium, comprising polyacetaldehyde dissolved in pyridine in thepresence of acetic anhydride, With an aqueous solution of sodiumbicarbonate in an amount at least suflicient for destroying the aceticanhydride and for precipitating said polymer, and recovering saidprecipitate, whereby stabilized pure elastomers having a decompositionstarting temperature of at least 125 C. are obtained.

10. Process according to claim 1 wherein said polymers are further heattreated at a temperature of between 300 C.

11. Process according to claim 2 wherein said polymers are further heattreated at a temperature of between 100- 300 C.

12. Process according to claim 7 wherein said polymers are further heattreated at a temperature of between 100 300 C.

13. Process according to claim 8 wherein said polymers are further heattreated at a temperature of between 100- 300 C.

14. Process according to claim 9 wherein said polymers are further heattreated at a temperature of between 100- 300 C.

15. The elastomeric polymer of acetaldehyde prepared in accordance withthe process of claim 1.

16. The acetic anhydride-modified elastomeric polymer of acetaldehydeprepared in accordance with the process of claim 7.

17. The elastomeric polymer of acetaldehyde prepared in accordance withclaim 10.

18. The acetic anhydride-modified elastomeric polymer prepared inaccordance with claim 12.

References Cited by the Examiner UNITED STATES PATENTS 2,989,509 6/1961Hudgin et al 260-67 3,001,966 9/1961 Funck et al 260-67 3,174,948 3/1965Wall et al 26045.8

SAMUEL H. BLECH, Primary Examiner. WILLIAM H. SHORT, Examiner. R. LYON,Assistant Examiner.

1. PROCESS FOR THE THERMAL STABILIZATION OF POLYMERS CONSISTING OFPOLYACETALDEHYDE ELASTOMERS OF HIGH MOLECULAR WEIGHT COMPRISING TREATINGSAID ELASTOMERS WITH A DISSOLVING AMOUNT OF PYRIDINE, ALLOWING THERESULTING SOLUTION TO STAND AT ROOM TEMPERATURE, ADDING AN ALKALINEAQUEOUS SOLUTION SELECTED FROM THE GROUP CONSISTING OF ALKALINE METALHYDROXIDE, CARBONATES AND BICARBONATES SOLUTIONS IN AN AMOUNT AT LEASTSUFFICIENT FOR PRECIPITATING EFFECT, THEN SEPARATING THE PRECIPITATEDPOLYMERS FROM SAID SOLUTION WHEREBY A STABILIZED POLYMER HAVING ADECOMPOSITION STARTING TEMPERATURE OF AT LEAST 85*C. IS OBTAINED.